Electrode Crossovers

ABSTRACT

In one embodiment, a touch sensor includes drive electrodes. The drive electrodes include drive electrode structures that are each coupled to an adjacent drive electrode structure by a first strip of conductive material. The touch sensor also includes sense electrodes. The sense electrodes include sense electrode structures that are each coupled to an adjacent sense electrode structure by a second strip of conductive material. The sense electrode structures are formed on a same layer as the drive electrode structures. The first or second strip of conductive material include one or more conductive crossovers that each couple two drive electrode structures to each other or couple two sense electrode structures to each other.

RELATED APPLICATION

This application is a continuation under 35 U.S.C. §120 of U.S. patentapplication Ser. No. 12/643,622, filed 21 Dec. 2009, which claims thebenefit, under 35 U.S.C. §119(e), of U.S. Provisional Patent ApplicationNo. 61/203,595, filed 26 Dec. 2008, which is incorporated herein byreference.

BACKGROUND

As touchscreens have gotten larger, the number of electrodes needed tosense touches on the larger touchscreens effectively has grown. Eachsuch electrode is coupled to a pin on a controller. As the number ofelectrodes grows, so does the number of pins on the controller, addingto the complexity of the controller and wiring to couple the controllerto the electrodes. In some prior touchscreens, electrode interpolationschemes have been used to increase the effective number of electrodes onthe touchscreen, without increasing the number of required connectionsto controllers. Such interpolation schemes may not provide desiredaccuracy in determining touch locations.

SUMMARY

Two different sets of electrodes in a touch sensitive device are formedto produce an electric field gradient from one end of the electrodes tothe other end when opposite ends of the electrodes are driven withdifferent voltages. A signal measuring cycle is performed by alternatelydriving the ends of one set of electrodes while using the other set ofelectrodes to receive signals. The roles of the sets of electrodes arethen reversed, such that the set that was driven is now used to receivesignals from the other set of electrodes. Optional reference signalsrepresentative of touch strength may be obtained by driving both sidesof one set of electrodes, and then both sides of the other set ofelectrodes. The signals obtained are then used to determine the touchposition on the touch sensitive device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are top views of two electrodes of an electrode layoutfor a touch sensitive device according to an example embodiment.

FIG. 1C is a top view of combined electrodes from FIGS. 1A and 1B.

FIG. 2 is a block circuit diagram illustrating connections and circuitryto interface with a touch sensitive device according to an exampleembodiment.

FIG. 3 is a block circuit diagram illustrating alternative connectionsand circuitry to interface with a touch sensitive device according to anexample embodiment.

FIGS. 4A and 4B are top views of two electrodes of an alternativeelectrode layout for a touch sensitive device according to an exampleembodiment.

FIG. 4C is a top view of combined electrodes from FIGS. 4A and 4B.

FIGS. 5A and 5B are top views of two electrodes of a further alternativeelectrode layout for a touch sensitive device according to an exampleembodiment.

FIG. 5C is a top view of combined electrodes from FIGS. 5A and 5B.

FIG. 6 is a table illustrating signals for detecting touch locations ona touch sensitive device according to an example embodiment.

FIG. 7 is a graph illustrating signals for horizontal measurement for atouch sensitive device according to an example embodiment.

FIGS. 8-13 are tables illustrating burst sequences used to obtainsignals to determine touch location according to an example embodiment.

FIG. 14 is a top view of a single layer electrode layout for a touchsensitive device according to an example embodiment.

FIG. 15 is a top view of an alternative single layer electrode layoutfor a touch sensitive device according to an example embodiment.

FIG. 16 is a table illustrating a proximity burst for detecting objectsproximate a touch sensitive device according to an example embodiment.

FIG. 17 is a top view of a single layer electrode layout having morethan two vertical axis electrodes according to an example embodiment.

FIG. 18 is an example circuit diagram illustrating connections to theelectrode layout of FIG. 17.

FIG. 19 is a table illustrating an example burst sequence for theelectrode layout of FIG. 17.

FIG. 20 is a top view of a single layer electrode layout having morethan two vertical axis electrodes according to an example embodiment.

FIG. 21 is an example circuit diagram illustrating connections to theelectrode layout of FIG. 20.

FIG. 22 is a table illustrating an example burst sequence for theelectrode layout of FIG. 20.

FIG. 23 is a top view of a single layer electrode layout having morethan two horizontal axis electrodes according to an example embodiment.

FIG. 24 is an example circuit diagram illustrating connections to theelectrode layout of FIG. 23.

FIG. 25 is a table illustrating an example burst sequence for theelectrode layout of FIG. 23.

FIGS. 26A and 26B are top views of two electrodes of a single layerelectrode layout having more than two vertical and horizontal axiselectrodes according to an example embodiment.

FIG. 26C is a top view of combined electrodes from FIGS. 27A and 27B.

FIG. 27 is an example circuit diagram illustrating connections to theelectrode layout of FIG. 26C.

FIG. 28 is a block diagram of a touch sensitive device includingcircuitry to interface with the touch sensitive device according to anexample embodiment.

DETAILED DESCRIPTION

The functions or algorithms described herein may be implemented insoftware or a combination of software and human implemented proceduresin one embodiment. The software may consist of computer executableinstructions stored on computer readable media such as memory or othertype of storage devices. Further, such functions correspond to modules,which are software, hardware, firmware or any combination thereof.Multiple functions may be performed in one or more modules as desired,and the embodiments described are merely examples. The software may beexecuted on a digital signal processor, ASIC, microprocessor, or othertype of processor operating on a computer system, such as a personalcomputer, server or other computer system.

First and second sets of electrodes in a touch sensitive device areformed to produce an electric field gradient from one end of theelectrodes to the other end when opposite ends of the electrodes aredriven with different voltages. The sets of electrodes form a matrixfrom which touch position may be obtained with minimal connections tothe matrix. A signal measuring cycle is performed by alternately drivingthe ends of the first set of electrodes, while using the other set ofelectrodes to receive signals. The roles of the sets of electrodes arethen reversed, such that the second set of electrodes are driven asabove with the first set used to receive signals. Reference signalsrepresentative of touch strength may be obtained by driving both sidesof the first set of electrodes, and then both sides of the second set ofelectrodes. The signals obtained are then used to determine the touchposition on the matrix of electrodes.

Several embodiments are described that create gradients of electricfields across electrodes formed of different materials. Some embodimentsutilize resistors external to a sensing area with electrodes formed ofhighly conductive material. In some embodiments, the resistivity is highenough such that undesirably large currents do not result when theelectrodes are driven to create the electric field gradient. Drive andreceive sequences are also described, along with algorithms fordetermining touch positions.

FIGS. 1A, 1B and 1C are top views of separate and combined electrodes ofa touch sensitive device 100 having a set of electrodes 110 exhibiting avertical field gradient and a set of electrodes 115 exhibiting ahorizontal field gradient. The electrodes in one embodiment are formedof highly conductive material such as copper. Many different highlyconductive materials may be used, including many metals and othermaterials that provide little resistance to electrical signals.

In one embodiment, the set of electrodes 110 include multiple rows ofhorizontally disposed diamond shaped structures that are coupledtogether at horizontal corners by strips of conductive material.Adjacent rows are coupled by a resistor, as indicated for example at120, coupling rows 122 and 124. In this embodiment, there are six suchrows, ending in a row 126, all connected to a resistive chain 128. Row122 is coupled to a conductive line 130, referred to as VERT0. Row 126is coupled to a conductive line 132, referred to as VERT1. In oneembodiment, lines 130 and 132 may be selectively coupled to drivecircuitry, and line 132 may be selectively coupled to sense circuitrywhich is not shown in FIG. 1. Conductors 130 and 132 are also coupledthrough the resistors between the rows of electrodes, such as resistor120. The resistive chain 128 operates as a resistive divider thatcreates an electric field gradient in the rows of electrodes in avertical direction when either of the VERT0 or VERT1 lines are drivenwith a drive voltage, with the other line held at a reference voltage,such as ground. Each resistor acts as an attenuator to reduce thevoltage applied to the next electrode, while end rows are driven with atthe drive voltage or are tied to the reference voltage.

A horizontal electric field gradient is produced in a similar manner incolumns of inter-connected diamond shapes corresponding to electrode set115. Outside columns are indicated at 140 and 142, and are coupled toconductive lines 144 (HOR0) and 146 (HOR1) respectively. The columns ofelectrodes are coupled together via a resistive chain 150, that includesresistors extending between the conductive lines 144 and 146, andcoupled to the columns to create an electric field gradient in thecolumns of electrodes in a horizontal direction when either of the HOR0or HOR1 lines are driven, with the other line held at a referencevoltage, such as ground. In some embodiments, the resistive chains maybe formed of discrete resistive elements.

The two sets of electrodes 110 and 115 form an electrode pattern thatappears as a grid of diamond shapes. The electrodes may be formed on thesame layer with insulated crossovers, or may be formed as two separatelayers separated by an insulating layer. Various conductive materials,such as ITO (indium tin oxide) and PEDOT (Polyethylenedioxythiophene)copper or silver paint (when used in fine line mesh patterns fortouchscreens) may be used to form the electrodes. The resistive chains120, 150 in one embodiment, form resistive bridges which create a smoothgradient of the electric fields in both the horizontal and verticaldirections. The resistive chains 120, 150 may be located outside edgesof the sets of electrodes.

FIG. 2 is a schematic representation of example circuitry 200 fordriving and receiving signals on the electrode pattern 100 of FIG. 1.Many different methods of driving and receiving signals may be employed,and circuitry 200 is just one example. Each of the lines VERT0 130,VERT1 132, HOR0 144, and HOR1 146 are driven by corresponding voltagesV0, V1, H0, H1. In one embodiment, line VERT1 is coupled to a sensecapacitor Cs0 at 210, which may be further coupled via a line labeled MVat 211 to a ramping resistor 216 for measuring transferred charge onCs0. Line HOR1 is coupled to a sense capacitor Cs1 at 212, which may befurther coupled via a line labeled MH at 217 to a ramping resistor 218for measuring transferred charge on Cs1. Circuitry 220 is coupled to theramping resistors to receive and measure the charge from the sensecapacitors. The ramping resistors are used for analog to digitalconversion, and may be replaced with other analog to digital convertersin further embodiments. In further embodiments, the sense capacitors maybe replaced by circuitry that may include integrators and operationalamplifiers, or other means of sensing charge. Circuitry 230 may also becoupled to lines MV 211 and MH 217 to switch the lines between areference voltage, floating, and charge transfer positions in accordancewith bursting sequences described below.

Circuitry 230 may be used to provide multiplexing of drive signals andto providing timing and control signals switch components during drivingand sensing of the device 100. Circuitry 230 may include amicrocontroller in some embodiments to provide control signals forproviding drive signals, sensing transferred charge, and for calculatingtouch positions. Circuitry 230 is representative of drivers to providethe drive signals, and receivers for receiving sensed signals fromelectrode patterns. One example circuit for driving and sensing may befound in U.S. Pat. No. 6,452,514.

In a further embodiment 300 in FIG. 3, sense circuitry, such as sensecapacitors 310 and 312 may also be coupled to line VERT0 130 and HOR0144 respectively. Performance of charge measurement may or may not bebetter than that provided by just using sense capacitors 210 and 212, asone capacitor coupled to each set of electrodes should suffice tocollect the transferred charge given the low resistance of theelectrodes in this embodiment. Further ramping resistors 320 and 322,used for analog to digital conversion, may also be used as shown in FIG.3 in conjunction with sense capacitors 310 and 312.

FIGS. 4A, 4B, and 4C are top views of separate and combined electrodesof an electrode layout 400, where the electrodes are formed using atransparent conductive material, such as ITO. In this embodiment, adiamond pattern is again formed, but using a conductive material thathas a resistance to it suitable for forming an electric field gradient.In this embodiment, sets of electrodes 410 and 415, are again formed asrows and columns of diamond shapes respectively, connected at corners bystrips of the conductive material.

The sets of electrodes 410 and 415 are coupled at each end by aconductive bar 420, 422, 424, 426 that does not result a significantelectric field gradient between adjacent rows or columns of each set ofelectrodes. Bar 420 is coupled to one end of each of the electrodes inelectrode set 415, and bar 422 is coupled to the other end of theelectrodes in electrode set 415. Bar 420 is coupled to a line 430,referred to as VERT0, and bar 422 is coupled to line 432, VERT1.Application of a voltage via line 430 VERT0, while line 432 VERT1 iscoupled to a reference voltage, results in an electric field gradientbeing formed along electrode set 415 between the ends coupled to bars430 and 432. An opposite gradient may be formed by providing a drivevoltage signal on line 432 VERT1 and a reference on line 430 VERT0. Bars424 and 426 are coupled to respective ends of electrode set 410, andalso to lines 434 HOR0 and 436 HOR1 to create a similar gradient wheneither line is driven and the other held to a reference.

FIGS. 5A, 5B, and 5C are top views of separate and combined electrodesof an electrode layout 500, where the electrodes are formed using atransparent conductive material, such as ITO. Layout 500 is similar tolayout 400, and utilizes the same reference numbers where elementsremain unchanged. In layout 500, the diamond pattern of shapes has beenmodified to increase the resistance as a row or column of electrodeshapes is traversed between bars. Cuts have been made in the diamondshapes to split them, and connect the split diamonds by a conductivepath, resulting in a higher resistance for each column and row. In oneembodiment, the electrode resistance is similar to that of a narrowstrip of material, similar in width to that of the strips connectingcorners of the diamond shapes in FIG. 4. In one embodiment, all the cutsare consistent to obtain a uniform pattern that results in a smoothelectric field gradient when the sets are driven. In other embodiments,the cuts may be varied to obtain other than a smooth gradient.

The layouts 400 and 500, as well as layout 100 may be driven and sensedin accordance with circuitry 200 or 300 as described above. Touchposition may be calculated by measuring the accumulated voltage on thesampling capacitors separately on two perpendicularly oriented sets ofelectrodes having electric field gradients on two layers. Driving oneend of one set and grounding the other end, creates a gradient of thefield across the set of electrodes which in one embodiment is smoothlymodulating sensitivity across the set of electrodes from maximum tozero. The signal is acquired from the other set of electrodes which worklike a single receiver plate. Then, the sets of electrodes are swapped,reversing the roles of the sets, so the other set is driven with theremaining set now operating as the single receiver plate.

Reference signals RH are obtained by driving both opposite sides of aset of electrodes (for example VERT0 and VERT1) and acquiring the signalon the opposite layer (HOR0 and HOR1). Driving in this manner removesthe gradient of the sensitivity across the surface of an electrode setsuch that the entire electrode set has equal sensitivity across theentire surface to work as a uniform, unitary capacitive key.

To get the complete XY position in one embodiment, six different drivesignals may be applied to different lines of the sets of electrodes. Inone embodiment, the drive signals take the form of bursts of voltagepulses that result in charge transfer from one electrode set to another.The amount of charge transferred may be affected by a touch. The signalsutilized in one embodiment are described in table form in FIG. 6. Thefirst column in FIG. 6 refers to a burst number, which each may includeone or more pulses of electricity. The order may be changed as desired.For each burst, the status of each of the connections, VERT0, VERT1,HOR0 and HOR1 are then described in subsequent columns. For example,during burst number 1, VERT0 is driven with the bursts, VERT1 is tied toa reference, such as ground, HOR0 is floating, and HOR1 is acquiringtransferred charge. The acquired charge is labeled in the next columnreferred to as signal. The signals, including references, acquiredinclude SV1, SV2, RV, SH1, SH3 and RH, where RV and RH are referencesignals from driving both ends of each set of electrodes.

There are several types of bursts for identifying a touch event. Someburst types measure the position along one axis of a sensing surface.For example, such a burst type may drive one end of electrodes spanninga sensing area and ground the other end, which creates gradient of thefield. A signal is acquired using electrodes spanning the sensing areain a different direction than the driven electrodes. These signals areshown in FIG. 6 as SV1, SV2, SH1 and SH2.

Another burst type measures the strength of a touch. Such bursts maysimultaneously drive both ends of a screen, converting the whole screeninto a capacitive key with the same sensitivity across the whole area.The acquired signal provides a reference to allow a more precisecalculation of touch position by reducing the effect of signal strengthon the reported touch location. It is understood that other burst typesare possible for sensing touch events without departing from the scopeof the present subject matter, including, but not limited to, bursttypes using mutual capacitance as discussed above and burst types usingself-capacitance to sense a touch event.

Burst number 1 in FIG. 6 measures a signal with a vertical gradienthaving a maximum signal on VERT0 to a minimum signal on VERT1. Burstnumber 2 measures the signal with the vertical gradient reversed, suchthat the maximum signal is on VERT1 with a minimum signal on VERT0. Inburst number 3, the signal is measured without a vertical gradientbecause both VERT0 and VERT1 are driven. In burst number 4, the signalis measured with a horizontal gradient, corresponding to a maximumsignal on HOR0 and minimum signal on HOR1. In burst number 5, thegradient is reversed, and in burst number 6, there is no horizontalgradient as both are driven.

The formulas for calculating the positions divide an area into two zoneswhere one of the signals is stronger than the other and each zone hasits own formula. The transition between the two formulas as a touchmoves between the two zones does not create a glitch because bothformulas yield the same result at the transition. The ideal signals fromhorizontal measurements between a point “X_(min)” and “X_(max)” on atouch sensitive device are shown in FIG. 7. FIG. 7 illustrates howsignal relationships change if the touch moves from a horizontalcoordinate X_(min) on the left of the touch sensitive device to ahorizontal coordinate X_(max) on the right side of the touch sensitivedevice. Point A is the value of RH at a particular touch point X0, B isthe value of SH1 at X0, and C is the value of SH2 at X0. A similar graph(not shown) represents how signal relationships change between SV1 andSV2 as a touch moves, for example, from a point “Y_(min)” at the bottomof a touch area to a point “Y_(max)” at the top of the touch area.

In various embodiments, a burst may provide a reference signal RHrepresentative of a horizontal position at an extreme edge of the area.In some embodiments, RH is a predetermined constant.

As stated above, for calculating a touch position including a horizontalcoordinate, the horizontal area of a touch screen, for example, isdivided into two zones. Horizontal zone 1 includes an area where the SH1field 715 is stronger than or equal to the SH2 field 720 (e.g. the areato the left of Xm, 710). Horizontal zone 2 includes the area where SH2is stronger than SH1.

Thus, when SH1 is bigger than or equal to SH2, the horizontalcoordinate, X, of a touch event is calculated as:

$X = {N_{h}( \frac{{RH} - {{SH}\; 1}}{{2*{RH}} - ( {{{SH}\; 1} - {{SH}\; 2}} )} )}$

where N_(h) is a scaling factor that can be used to provide a givenrange of coordinate values between positions X_(min) and X_(max) whenX_(min) is zero.

When SH2 is bigger than SH1 the horizontal coordinate, X, is calculatedas:

$X = {N_{h}( {1 - \frac{{RH} - {{SH}\; 2}}{{2*{RH}} - ( {{{SH}\; 1} + {{SH}\; 2}} )}} )}$

To calculate a vertical coordinate of a touch event, signals SV1, SV2and RV are used. The vertical area of a touch sensitive area is dividedinto two zones. Vertical zone 1 includes an area where the SV1 field isstronger than or equal to SV2 field. Vertical zone 2 includes the areawhere SH2 is stronger than SH1.

When SV1 is bigger than or equal to SV2 a vertical coordinate, Y, of atouch event is calculated as:

$Y = {N_{v}( \frac{{RV} - {{SV}\; 1}}{{2*{RV}} - ( {{{SV}\; 1} - {{SV}\; 2}} )} )}$

where N_(v) is a scaling factor that can be used to provide a givenrange of coordinate values between positions Y_(min) and Y_(max).

When SV2 is bigger than SV1 a vertical coordinate, Y, of a touch eventis calculated as:

$Y = {N_{v}( {1 - \frac{{RV} - {{SV}\; 2}}{{2*{RV}} - ( {{{SV}\; 1} + {{SV}\; 2}} )}} )}$

where, with reference to FIG. 6,

-   SV1 is the signal measured during burst #1.-   SV2 is the signal measured during burst #2.-   RV is a reference signal measured during burst #3.-   SH1 is the signal measured during burst #4.-   SH2 is the signal measured during burst #5.-   RH is a reference signal measured during burst #6.

In some embodiments, RH and RV need not be used. RH and VH, when used,provide the ability to determine touches accurately across the screen.The errors would generally be largest at the edges of the screen. Infurther embodiments, a weighted average formula may be obtained from theabove formulas for calculating positions. One example formula forcalculating the X coordinate of a touch event may be written as:

X=N _(h)(1*(RH−SH1)+2*(RH−SH2))/(2*RH−(SH1+SH2)−)−M.

Example burst timing compositions for each of the above bursts of FIG. 6are now described with reference to FIGS. 8-13. Burst sequence numberone of FIG. 6 is shown expanded in FIG. 8. Bursting of pulses is done onV0, with V1 connected to GND or another reference voltage, while HO isleft floating. Measuring is performed on H1, corresponding to thesignals from a first vertical gradient. As previously indicated, theacquisition bursts described herein are just one example of drivesignals that may be used. Many other drive signals and chargeacquisition methods may be used in further embodiments.

At a first step in FIG. 8, referred to as an initial discharge state,all capacitors are fully discharged. V0, MV, V1, H0, MH, and H1 areinitially coupled to ground (as represented by a ‘0’ in the table), orother reference voltage. At step 2, MV, HO and H1 are allowed to float(as represented by a ‘F’ in the table). At step 3, charge is transferredfrom V0 (by driving pin V0 high, as represented by a ‘1’ in the table)and accumulated on sense or sampling capacitor Cs1. At step 4, MH isallowed to float, floating Cs to end the charge transfer. At step 5, H1is coupled to ground to discharge parasitic capacitance, Cp. At step 6,V0 is coupled to ground, discharging the unknown capacitance, Cx. Atstep 7, H1 is allowed to float to prepare for the next transfer. At step8, MH is grounded to ground Cs to prepare for the next transfer. At step9, steps 3-8 are repeated N times until the acquisition burst iscompleted, where ‘N’ is a predetermined number designed to provide atargeted amount of signal gain and noise suppression by virtue ofrepetitive signal accumulation; ‘N’ in the context of this and furthertable figures herein, may be any integer number and may also includezero. At step 10, MH is floated to prepare for the measurement. At step11, MN is coupled as an analog comparator input, and H1 is coupled toground. At step 12, the CHRG line to the sense circuitry is coupled toperform measurement of the signal via ramping of the voltage on thesample capacitor(s) via a resistor such as 216, until the voltage on thesample capacitor reaches a predetermined voltage, the measurement beingtaken by timing the interval required to reach the predeterminedvoltage. The above explanations apply also similarly to FIGS. 9 through13 with modifications as will be discussed below.

The floating states are used explicitly in some embodiments to avoidcross-conduction when output drivers of pins switch on and off. In somemicrocontrollers, during transitions between floating and output statesand vice-versa while one pin is “semi output”, another connected to theother side of a sampling capacitor is also “semi output”. The result canbe a significant, unpredictable and thermally dependent amount of chargebeing destroyed on the sample capacitors due to such cross-conduction.However, the burst sequences will operate adequately if floating statesare not expressly used as shown in the various table figures in someembodiments, specifically if the output drivers avoid suchcross-conduction by their intrinsic design.

Burst step number 2 of FIG. 6 is expanded as illustrated in FIG. 9. Thisstep consists of bursting pulses on V1, with V0 connected to GND whileH0 is floating, with measuring performed on H1 to acquire a secondvertical gradient.

The individual steps illustrated in FIG. 9 are similar to those in FIG.8 as discussed supra, except that in step 3, charge is transferred frompulses on V1 instead of V0.

Burst step number 3 of FIG. 6 is expanded as illustrated in FIG. 10.This step consists of bursting pulses on both V0 and V1 with H0floating, while measurement is performed on H1. This acquires signalwithout a voltage gradient, so that the entire screen responds as asingle unitary ‘key’ without differentiation as to touch position. Asdiscussed, the signal resulting from this step is used as a reference RVin order to make position calculations along the vertical axis moreprecise by reducing the influence of signal strength variations.

Burst step number 4 of FIG. 6 is expanded as illustrated in FIG. 11.This step consists of bursting pulses on H0, with H1 connected to GNDwith V0 floating, while measurement is performed on V1 in order toacquire signal with a first horizontal gradient.

Burst step number 5 of FIG. 6 is expanded as illustrated in FIG. 12.This step consists of bursting pulses on H0 while H1 is connected to GNDand V0 is floating, with the measurement being taken on V1 in order toacquire a second horizontal signal gradient.

Burst step number 6 of FIG. 6 is expanded as illustrated in FIG. 13.This step consists of bursting pulses on H0 and H1 while V0 is floatingwhile measuring signal on V1. This acquires signal without a voltagegradient, so that the entire screen responds as a single unitary ‘key’without differentiation as to touch position. As discussed, the signalresulting from this step is used as a reference RH in order to makeposition calculations along the horizontal axis more precise by reducingthe influence of signal strength variations. Each of sequences numbers4, 5, and 6 correspond closely to sequences 1, 2, and 3 respectivelyexcept that opposite sets of electrodes are driven and sensed.

Using a single layer ITO design in one embodiment may result in one ormore advantages like reduced cost, increased reliability, higher yieldrate, etc. Also, the difference between the gains in the measurements onthe top and the bottom layer will become minor since such aconfiguration has no Z-axis layer displacement. One solution for usingITO for such touch screen is shown on FIG. 14. The whole design isformed of multiple substantially parallel lines.

Half of the lines 1410 are used to create a horizontal gradient betweenconnectors HOR0 and HOR1. Lines 1410 may utilize externally connectedresistors 1415. In some embodiments, resistive structures may be formedof ITO or other resistive material. The other half of the lines 1420 areused to create a vertical gradient between VERT0 and VERT1. Lines 1420may be connected in parallel. When using equal thickness lines it ispossible that the resistance of the lines 1420 connected in parallel maybe low, resulting in a sub-optimal vertical gradient.

In FIG. 15, lines 1510 used to form a vertical gradient are madenarrower than the lines 1410 used to create the horizontal gradient. Toobtain 2K resistance across 10 vertical bars in parallel between VERT0and VERT1 the resistance of each bar should be 20K in one embodiment.Other resistances may be used in further embodiments. Also, using ahigher resistance ITO layer will help to increase the resistance betweenVERT0 and VERT1 to a desired range. In further embodiments, zigzagpatterns (not shown) may be used to increase the resistance of the barsconnected between VERT0 and VERT1. It is understood that other methodsand circuits for mutual capacitance type touch event sensing arepossible without departing from the scope of the present subject matter.In addition to charge transfer circuits and method used for exampleherein, other methods include, but are not limited to, amplitudedetection, RC time constant measurements, modified charge transfermethods, charge transfer methods using filtering such as ‘leakyintegrators’ having an asymptotic response, and combinations thereof.

Various embodiments of the disclosed electrode patterns allow variousmethods of touch event detection, including various methods of proximitydetection. One form of proximity detection may be accomplished usingself-capacitance, instead of mutual capacitance as described above.Proximity detection using self capacitance is possible because selfcapacitance field lines freely radiate outward into free space from theelectrodes. A four electrode touch screen according to variousembodiments of the present subject matter allows simple implementationof proximity detection by issuing on regular intervals, parallel burstson both channels. A self capacitance type proximity burst is shown inFIG. 16, which is used in conjunction with the circuit of FIG. 2. Aparallel burst on two channels is provided by keeping CHRG, V0 and H0floating during the burst, allowing the field lines to propagate awayfrom the surface of the screen. It is understood that other methods ofself-capacitance proximity sensing are also possible without departingfrom the scope of the present subject matter, for example, but notlimited to, RC time constant sensing.

Proximity detection acquisitions using self-capacitance maybe combinedwith mutual capacitance acquisitions in various ways. For exampleproximity bursts may be suspended when a touch is detected on thesurface, as additional proximity detection consumes processing resourcesthat may be available for, among other things, identifying the locationof the touch event. In other instances it would be desirous to acquirein both mutual and self capacitance modes, for example when it is notyet clear that a finger has touched the screen surface, eg when signalsindicate an ambiguous condition. In yet another condition, it would bedesirable to only sense using self-capacitance in a proximity detectingmode when the signals from self-capacitance are weak, eg, when it isclear there is no touch present on the screen surface. The ratio ofself-capacitance to mutual capacitance acquisition bursts over time canbe adjusted to suit various signal conditions in order to optimizeresponse time and power consumption.

Normally, the touchscreen design utilizes a shape of the screen that isrectangular, not square. Using only four electrodes on rectangularshaped screens can make the resolution and/or the linearity across the Xand Y directions more or less unequal. For higher aspect ratio screens,it is desirable to maintain a consistent resolution and linearity alongeach axis. One solution is to add more electrodes in one of thedirections. One of the possible designs is to use five electrodes, twoto detect the position in the horizontal direction, and three to detectthe position in thevertical direction as indicated in layout 1700 inFIG. 17 and corresponding connections in FIG. 18. Layout 1700 in oneembodiment is formed of resistive electrode material that is formed intwo sets of parallel lines in a single layer, forming horizontal andvertical electric field gradients when driven. In this embodiment, Cs0is shown coupled to VERT1, but in further embodiments, Cs0 may becoupled to VERT0 or VERT2.

In order to get enough information to calculate the touch position andto compensate the offsets the design of FIG. 18 employs seven differentacquisition burst steps as illustrated in FIG. 19, with the additionalburst over that of FIG. 6 being used to measure signal from drivingVERT2. To obtain touch position in the horizontal direction, threebursts, 5, 6, and 7 are used. To obtain position in the verticaldirection, four bursts, 1 through 4, are used. Notice that the designstill utilizes just two sampling capacitors and two conversion rampingresistors. Other methods and circuitry to detect a touch position arepossible without departing form the scope of the present subject matter.For example, in some embodiments, the ramping resistors may be omittedwhen using an alternative analog to digital converter to measureaccumulated charge or when using an operational amplifier chargeintegrator in place of capacitors Cs.

Because the design may be made using two sampling capacitors (one forhorizontal and one for vertical measurements) there will be nodifference in the gain between different channels measured on the samesampling capacitor, resulting in improved linearity.

With respect to FIG. 17, additional electrodes may be added in thevertical direction without the need to add more Cs sampling capacitors.Additional electrodes may be added to the vertical direction in similarfashion.

FIG. 20 shows a six electrode design 2000 on single layer ITO, wherefour electrodes, VERT0 to VERT3 are used on the vertical axis.Connections are shown in FIG. 21, illustrating the use of two samplingcapacitors.

The six electrodes touch screen utilizes eight different bursts. Thebursts are shown in FIG. 22. Compared to the burst sequence table ofFIG. 19, additional bursts are used to measure signals from drivingadded electrode VERT3. As illustrated in conjunction with FIGS. 17, 18,19, 20, 21 and 22, electrodes may be added in along at least one axiswhile still using only one Cs sample capacitor per axis.

In still further embodiments, more electrodes may be added in bothdirections as illustrated in FIG. 23 at layout 2300 and correspondingconnection diagram in FIG. 24. In this case the whole screen is dividedinto two lateral sections which work in a similar way to layout 2000;the left and right VERTn halves are connected in identical fashion tothe same circuit lines so that the two halves behave as though they werecontinuous across the screen, but for the brief interruption of the HOR1spine. The burst sequence consists of nine bursts as shown in FIG. 25.One difference is that there will be one additional burst in thehorizontal direction as shown in step 8, resulting in 9 steps.

The design 2300 results in nonlinearity in the horizontal directionbecause of the resistance of the vertical spine extending between thetwo terminals labeled HOR1 as shown in FIG. 23. It is possible tocompensate for such non linearity in software, however by decreasing theeffective resistance of the spine by widening it or by the use of amaterial that augments conductivity along its length, the linearity canbe substantially improved. However, increasing the thickness of themiddle bar beyond some limit will create localized linearity problems.The middle bar may also be formed at least in part of highly conductivemetal in some embodiments to reduce its resistivity. In one embodiment,Cs1 is coupled to the middle bar via HOR1 to collect transferred charge.Cs1 may alternatively be coupled to HOR0 or HOR2 in other embodiments.CS0 is shown coupled to VERT1, but may also be coupled to any of theother VERTn connectors in further embodiments.

FIGS. 26A, 26B, and 26C are top views of separate and combinedelectrodes of a seven electrode design at 2600 with two layers of ITO,or other suitable material. If the layers are formed on different sidesof a substrate, such as PET, as long as the two layers are close to eachother there will be little difference in the sensitivity on bottom andtop side measurements. In various embodiments, PET used in the ITOdesigns is no more than 125 um thick and preferably 50 um thick. FIG. 27illustrates the connections that may be used with design 2600.

In some embodiments, electrode design 2700 may be used to form up to sixdifferent sensitive areas defined by pairs of vertical and horizontalconductive lines. In other words, the area of the design 2600 bounded byVERT0, VERT1, HOR0 and HOR1 may be treated as one area, and other areaswill correspond to other pairs of vertical and horizontal conductivelines. In this manner, touches in separate areas may be independentlydetected, even if occurring at the same time. This mode of operation maybe referred to as a ‘multi-touch’ mode of operation. Additional sensecapacitors may be used in further embodiments if desired. Burstingsequences may be changed in further embodiments to accommodate amulti-touch mode of operation.

In various embodiments, a four electrode touch sensitive device offersextreme simplicity of design, using two sampling capacitors and tworamping resistors. The ramping resistors may be omitted, instead usingan ADC converter, perhaps together with an operational amplifierintegrator.

The high speed, good resolution and linearity, and the ability to detectprecisely the touch location will allow such devices to be used in lowcost character recognition devices, including electronic writingtablets, for example. The low number of wires connecting the sensingcircuit to the touch screen electrodes allows for a narrow border,permitting a more optimal use of front panel space. The connection tothe screen is also simplified because of the low number of wires.

FIG. 28 is a block schematic diagram of a touchscreen 2800 andassociated touch screen controller 2805 according to an exampleembodiment. Touchscreen 2800 is representative of a touch sensitivedevice that may be used to provide an interface to different devices.Touchscreen 2800 includes sets of electrodes 2810, 2815 coupled at eachend by a bar 2820, 2822, 2824, 2826. In various embodiments, each bar isof significantly higher conductivity than the screen electrodesthemselves, so as not to create a significant electric field gradientbetween adjacent rows and columns of each set of electrodes; forexample, these bars could be made of metal, while the electrodes aremade of ITO. Each bar is coupled to both an input 2860 and an output2862 of the controller 2805 to sense touch events of the touchscreen2800.

In various methods of sensing touch events, each of the electrodes iselectrically excited using the outputs of the controller, and sensedusing the inputs of the controller. The controller includes severalinput and output components to assist in timing the excitation andsensing of the electrodes. Input components include sample-and-holdcircuits 2864, an analog multiplexer 2866 and an analog-to-digitalconverter 2868. Samplers 2864 are also embodied as the Cs capacitorsshown in the various figures herein, for example Cs0, Cs1, Cs2, and Cs3of FIG. 3. While four samplers are shown, in many instances only twosamplers are required, for example when using the topology shown in FIG.2. Output components includes timing logic 2870 coupled to the inputcomponents to time and generate output signals in coordination with thesensing functions of the input components. Electrode drivers 2871generate the excitation of the electrodes 2810, 2815 in response to thetiming logic circuit 2870. Individual drivers at 2871 each have a3-state capability in order to implement the floating states associatedwith the various burst sequences described in conjunction with thevarious circuits and tables discussed above, in addition to being ableto drive to at least one reference voltage. A signal processor 2872acquires and processes sensed signals from the ADC 2868. Touch eventsand location information is passed to a controller interface 2874.Master control logic 2876 is coupled to the interface 2874, timing logic2870 and signal processor 2872 to provide over-all control andmonitoring of the touch screen controller 2805. In various embodiments,the controller interface 2874 exchanges touch event information andstatus with a host device 2878.

The controller interface 2874 acts to process signals to and from acommunication protocol for communicating with the host 2878. In someembodiments, a serial protocol such as serial peripheral interface (SPI)or inter-integrated circuit (I2C) may be used. Various other protocolsmay be used in further embodiments.

1. A touch sensor comprising: a plurality of drive electrodes comprisinga plurality of drive electrode structures each coupled to an adjacentdrive electrode structure by a first strip of conductive material; and aplurality of sense electrodes comprising a plurality of sense electrodestructures each coupled to an adjacent sense electrode structure by asecond strip of conductive material, the plurality of sense electrodestructures being formed on a same layer as the plurality of driveelectrode structures, the first or second strip of conductive materialcomprising one or more conductive crossovers that each couple two driveelectrode structures to each other or couple two sense electrodestructures to each other.
 2. The touch sensor of claim 1, wherein atleast a portion of one or more of the conductive crossovers is disposedin a separate layer from the drive or sense electrodes.
 3. The touchsensor of claim 2, further comprising insulating material separatingeach of the conductive crossovers from conductive material of anadjacent electrode.
 4. The touch sensor of claim 3, further comprisinginsulating material separating each of the conductive crossovers fromconductive material of an adjacent electrode, the adjacent electrodebeing one of the plurality of drive or sense electrodes different fromthe plurality that comprises the conductive crossovers.
 5. The touchsensor of claim 1, wherein each of the electrode structures comprises aconductive mesh of lines of conductive material.
 6. The touch sensor ofclaim 1, wherein the conductive material comprises copper or silver. 7.The apparatus of claim 1, wherein the drive and sense electrodestructures comprise substantially diamond-shaped electrode structures.8. A device comprising: a touch sensor comprising: a plurality of driveelectrodes comprising a plurality of drive electrode structures eachcoupled to an adjacent drive electrode structure by a first strip ofconductive material; and a plurality of sense electrodes comprising aplurality of sense electrode structures each coupled to an adjacentsense electrode structure by a second strip of conductive material, theplurality of sense electrode structures being formed on a same layer asthe plurality of drive electrode structures, the first or second stripof conductive material comprises one or more conductive crossovers thateach couple two drive electrode structures to each other or couple twosense electrode structures to each other; and a computer-readablenon-transitory storage medium embodying logic that is configured whenexecuted to control the touch sensor.
 9. The device of claim 8, whereinat least a portion of one or more of the conductive crossovers isdisposed in a separate layer from the drive or sense electrodes.
 10. Thedevice of claim 9, further comprising insulating material separatingeach of the conductive crossovers from conductive material of anadjacent electrode.
 11. The device of claim 10, further comprisinginsulating material separating each of the conductive crossovers fromconductive material of an adjacent electrode, the adjacent electrodebeing one of the plurality of drive or sense electrodes different fromthe plurality that comprises the conductive crossovers.
 12. The deviceof claim 8, wherein each of the electrode structures comprises aconductive mesh of lines of conductive material.
 13. The device of claim8, wherein the conductive material comprises copper or silver.
 14. Thedevice of claim 8, wherein the drive and sense electrode structurescomprise substantially diamond-shaped electrode structures.